Smokers who lit up within half an hour of waking up were at a 59 percent higher head and neck cancer risk and 79 percent elevated lung cancer risk compared with those who waited at least an hour, Joshua E. Muscat of Penn State College of Medicine in Hershey, Penn., and colleagues found.

Those who started on their first cigarette 31 to 60 minutes after waking were at significantly elevated risk as well (42 percent and 31 percent, respectively), the group reported in two linked studies appearing online in Cancer.

While any smoking boosts cancer risks, an early start in the day might be particularly risky because it signals stronger nicotine dependence, the researchers suggested.

Thus, "smokers who smoke soon after waking may require special efforts to make them aware of their increased risk and the need for smoking cessation therapies," Muscat's group wrote.

They compared cancer risks similarly in two cohorts, reported separately.

One study described results among 1,055 head and neck cancer patients and 795 controls, all with a history of smoking cigarettes, seen at New York-area academic center hospitals.

Similar to the pack-years smoked adjusted results above, head and neck cancer risk followed time to first cigarette after adjustment for number of cigarettes smoked per day.

The other study described analysis of 4,775 newly-diagnosed lung cancer cases and 2,835 controls, all former or current cigarette smokers, seen at the same group of academic hospitals.

Current smoking and greater number of cigarettes smoked per day were linked to higher lung cancer risk.

As with the sociodemographic and pack-years adjusted risks noted at the outset, lung cancer risk controlling for number of cigarettes smoked per day rose significantly with an earlier start in the day.

"Because the risk was calculated among ever-smokers, the odds ratios were substantially lower than what is typically observed in studies that include never-smokers," the researchers noted.

Results were similar in other analysis stratified by years since quitting and current smoking status.

The researchers cautioned that case-control results can be limited by recall bias, measurement error, and confounding.

Time to first cigarette was reported on a single occasion and may have changed over time, they added.

Another limitation was the small number of minority patients in the head and neck cancer analysis, which may impact generalizability.